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Show -8- Th.e appropriate design procedure can be done in the following way. Without ~oln.g t~ the root of the matter, we can consider the interaction between the ~,nsplratlon p'rocess and flow conditions with significant hydraulic resistance as a black bo~, a~d a very long flare pilot can be considered as involving two parts: a regular InspIrator and a long mixture tube. In.spiration c~n be calculated by equation 1, used for regular inspirating burners wIth short mIxture tubes. Then, the excess air factor's empirical dependence on mixture tube pressure drop, n = ~Ll.p(), can be used to enter a correction for the value n, obtai ned from equation 1. The function n = ~Ll.p() can be presented as dimensionless. See fig. 4 ("Excess Air Factor vs. Pressure Drop"). This allows the use of the design procedure for mixture tubes of different lengths and diameters in English or metric measurements. Inspiration calculations carried out on the basis of this developed design procedure demonstrate good accuracy. The average design error for flare pilots in the range of lengths up to 100 ft was 5 percent. Fig. 5, with equations 2 thru 5, depicts the appropriate design procedure steps. Assuring Reliable Ignition A constant burning pilot flame is essential since any gas vented from a flare must be ignited. Pilot ignition systems have come a long way in recent years. It wasn't so long ago that major companies were using flaming arrows, burning rags on pulleys and other primitive ignition methods. The most common ignition system is a flamefront generator with remote ignition panel, developed in the 1940s by a major oil company. While there are certain misconceptions about the operation and reliability of these panels, they usually can be attributed to a limited working knowledge and/or an improper installation. Air and fuel gas are metered through orifices in the remote ignition panel to form a combustible mixture; then a spark is introduced to generate a flame which is delivered through a 1" diameter pipe to the flare pilot, safely and quickly. When there are multiple flare pilots, there are either valves to direct flamefronts to each pilot or a manifold to direct a single ball of flame to all pilots at the same time. The ball of flame travels thru the pipe with the combined velocity of the gas/air mixture [approximately 88 ftls (27m/s)]. With natural gas, the burning speed of the flame is 75 ftls (23 m/s). The flamefront arrives at the top of the flare stack |